Turbine



Feb. 22, 1949.

G. K. W. BOESTAD ET AL TURBINE 2 Sheets-Sheet 2 Filed Nov. 10, 1943Pstentedl-ea 22, 1949` -UNITED STATI-:s Pa'rlalvr o FICE l 'rUnBrNEGustav Karl William Boestad and Erik Otto Eriksson, Lidingo, Sweden,assignors, by mesne assignments, to Jarvis C. Marble, New York, N. Y.,Leslie M. Merrill, Westfield, N. J., and Percy H. Batten, Racine, Wis.,as trustees Application November 10, 1943, Serial No. 509,800 In SwedenJanuary 16, 1943 3 Claims. (Cl. 60.41)

structions with austenitic steel it will be found dimcult, for instancevin gas turbines, to maintain the small clearances between theirrotating and stationary parts which are necessary particularly in gasturbines of the react-ion type in order to maintain a good efiiciency.The heat conductivity of the material has the effectthat a low rate ofheat conductivity involves large temperature differences bewteen thevarious parts of the turbine when the temperature of the gas is changed,which frequently takes place rapidly when the turbine is `started orstopped. Particularly when the turbine is brought to a stop, the rotorthereof will keep warm for a longer time than the remaining parts, andwhen the turbine housing is cooled down and contracts, the clearancesmay be taken up to a. high degree, if the heat conducting capacity ofthe material is low. Even with atemperature difference of only 200 C.and with a diameter of the blade Arim of 1 metre, the difference in heatexpansion between the housing and the rotor will be above 3 millimetreswith austenitic steel.

This object of the invention is to improve tur\ bines of the abovementioned kind, so that the favourable properties for instance ofaustenitic steel may be fully utilized. This is accomplishedsubstantially by the fact that the blades of the turbine consist,entirely or in part, of a material of great heat resisting properties,and that the rotor is made from another material having a lowercoeilicient of heat expansion than that of the rst-mentioned material,the turbine being provided with means for. cooling the rotor. The rotoris preferably-of a material having a higher heat conductivity as wellesta lower coeiiicient of heat expansion than the blades. The blades maybe made from austenitic steel, and the rotor and the housing may be madefrom steel of the martensitic type, which is comparatively cheap and hasa low coefllcient of heat expansion. The blades occupy a relativelysmall portion .of the radial extent 'of a turbine.. by reason ofwhichthe greater heat expansion on' the part of the blades is of nopractical importance. Add to circumstances rapidly follow any change` inthe temperature of the driving medium. This produces the result that thegreater coeilicient of heat expansion of the blades, whenlthe turbine isstopped, aids in increasing the clearances between the blades and thehousing, which is an advantage. The average stress in a blade willalawys be comparatively low, and for this reason l it will be lessimportant to provide cooling of the blade in consideration of theshrinkage of the blade material. By the fact that the rotor is cooledand ismade from steel-having a good heat conductivity, it will be keptat a temperature at which it is still in possession of its good strengthproperties. Moreover, the disadvantages of expansions of different sizeswith respect to the rotor and the housing at changes in temperatures areobviated to a great extent.

'I'he invention will be described more fully hereinafter with referenceto a few forms of' embodiments illustrated by way of example in l theaccompanying drawings.

Fig. 1 is 'a horizontal view, partly in section, through a gas turbineconstructed according to the invention.

Fig. 2 shows the portion of the turbine framed by the lines 2 in Fig. 1,on an enlarged scale.

Fig. 3 shows a gas turbine according to a further embodiment and in thesame view as in Fig. 1.

In Fig. 1, I0 designates generally a rotor, which is composed of anumber of turbine disks I2, the inner diameter of which is spaced fromthe axis of rotation, so that an inner axial passage or bore I4 isformed. The disks I2 are connected with one another, preferably throughwelding, both at the inner and at the outer `axial passages 2 2, whichare disposed alternately onV different radii, and are adapted to connect`the various spaces 20 with-each other.

yThe disks I2 of the rotor carry blades 24 which are arranged, togetherwith guide blades 26 secured in the turbine housing 8, in a passage 30having the gaseous working medium owing therethrough. The outermostlturbine disk I2 lon the left hand side in- Fig. 1 (the high pressureside of the turbine) may, over a preferably conical portion 32, be madeintegral with a shaft `34 this that the surface ofthe bladesis so large.

relative to the weight of the, material thereof and relative to thecoefllcientof heat transfer at the` surface, that the blades will underall cooperating in known manner With'radial and axial thrust bearings 35secured in the turbine housing. Provided between vthe portion 32 and theshaft 34 arepacking members 36 and 38, re-

spectively, on both sides ofthe bearings 35. The

"outermost disk l2 on the opposite side of the 54, the cooling air owsthrough the passages 22 to the spaces in the rotor, a relative rotarymovement being thus produced between the cooling air and the walls ofthe turbine disks, so that high coefficients of heat transfer areobtained. Thi cooling air then enters the passage I4 closed at bothends, and continuesthrough a radial passage 56 in the first turbine diskI2 at the high pressure end of the rotor, whereupon the cooling air isintroduced into the clearance 58 behind the rst guide blade rim 26 so asto be taken up by the current of driving medium flowing through thepassage 30. The clearance 58 is separated from the space 54 by means ofpackings 60.

The cooling air is taken out at such a point on or behind the compressorthat at the entrance into the interior of the rotor it has a pressurewhich is somewhat higher than the pressure in the clearance 58.

The rotor I0 and the disks I2, respectively, are made from a steel whichis comparatively cheap, possesses a good heat conductivity'and a lowcoeiiicient of heat expansion. such steels are for instance those of themartensitic type. able steel of this kind has a comparatively smallpercentage of chromium, that is to say M75-2.5%,

' while the percentage of molybdenum amounts to 0.31%. The Ablades 24,on the other hand, are,

at least on the high pressure side of the rotor,

made from a more expensive steel, having very great heat resistingproperties, primarily from an austenitic steel having a high percentageof nickel and chromium and preferably also containing tungsten. A steelof this type withstands,

for instance at 600 C., a stress of 4 kilograms per square millimetre,without creeping or expanding permanently by more than 1% of its lengthin 100,000 hours.

The turbine housing 28 is preferably made, entirely or in part, from thesame material as the rotor I0, or from a material equivalent thereto asfar as the coe'cient of heat expansion is concerned. The guide blades 26may be secured in rings 21 (Fig. 2), which are made from the samematerial as the blades 24. These rings, which are inserted into thehousing 28, have a greater extent in axial direction than the guideblades, so that they will, approximately at least, form the outerbounding wall of the passage 30 so as to protect the housing against thehot working mediuin flowing through the passage. Inasmuch as they have,in addition thereto, a heat expansion capacity lower than that of thehousing, they will exert a braking eifect yon the flow of heat to thehousing. Aiding in this is also the fact that the portion of the rings21 in which the guide blades are secured has little thickness and isspaced from the Wall of the housing. A sheet metal partition 3| may beprovided in known manner in the inlet of the turbine, said partitionhaving a cooling medium A suitflowing over it on the outside, suchmedium preferably consisting of air taken vfrom the compressor andhaving a lower temperature than that of the working medium inside saidwall.

By making the various parts of the turbine from such materials, combinedwith the cooling of the rotor, which may be effected in the manner abovedescribed, the advantages already described will be gained.

4The embodiment according to Fig. 3 differs from the preceding onesubstantially only in that the rotor I0 is made with an integralbladecarrying member. This member is provided with axial passages 62 forthe cooling air extending therethrough, which are situated outside theaverage radius of the rotorand near the points of attachment of theblades 24. The passages 62 are not through-passages at the right handend of the rotor I0 in the drawing, but communicate through radialpassages 64 with the central passage I4. The cooling air is conveyedfrom the annular space on bore 48 to the space 54 through .passages 66,68 in reinforcing members 10 located in front of the rst guide blade andin the housing 28, respectively. To increase the coeicient of heattransfer in the passages 62, it is possible to lead the cooling air intothe same, so that it will attain a rotary movement at a higher velocitythan corresponding to the average velocity in the passage. The sameeffect may be attained by means of insertions in the passages, sodevised that the area of the passage is reduced, without the coolingsurface being diminished.

While different embodiments of the invention have been shown, it is tobe understood that these are for purpose of illustration only, and thatthe invention is not to be limited thereby, but its scope is to bedetermined by the appended claims.

What We claim is:

1. In a turbine, a rotor having a blade carrying structure and bladescarried by said structure, said blades and said blade carrying'structurebeing of different materials, the blade material being an austeniticsteel and the material of the blade carrying structure being amartensitic steel, and means for cooling the blade carrying structure ofthe rotor.

2. In a turbine, a rotor having a blade carrying structure and bladescarried by said structure and a housing structure around said rotor,said structures being constructed of martensitic steel and said bladesbeing constructed of austenitic steel and means for .cooling the bladecarrying structure of the rotor.

3. A turbine as set forth in claim 2, in which the housing structurecarries'guide blades extending between the rotor blades and in which theguide blades are secured in rings of austenitic steel.

GUSTAV KARL WILLIAM BOESTAD. ERIK OTTO ERIKSSON.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS

